1. Field of the Invention
The present invention relates to a substrate processing apparatus for processing a substrate using a processing liquid.
2. Background Art
US 2011/0132465A1 discloses a substrate processing apparatus which processes a substrate using a processing liquid stored in a tank.
In some cases, a tank for storing a processing liquid is provided with a level sensor for detecting the level of the processing liquid at a predetermined level. The level sensor outputs a signal indicating, e.g., whether the level of the processing liquid in the tank is below or above the predetermined level, and this signal is used to determine whether or not to replenish the processing liquid in the tank. If this level sensor fails, however, the processing liquid cannot be timely replenished. Therefore, it is necessary to detect the failure of the level sensor.
In order to detect and address the failure of the level sensor, the tank may be additionally provided with a low level sensor for detecting the level of the processing liquid in the tank at a level which is lower than the above predetermined level. However, such a low level sensor is liable to corrode quickly, since it is continuously immersed in the processing liquid for long periods of time. This means that a short replacement cycle is required for the low level sensor, thus resulting in increased operating cost.